Firing a Propane Kiln in Canadian Winters

After a long hiatus from pottery, I'm attempting to get a studio up and running again (shed is built and sided, just need a roof and some power - it's getting exciting!). At one time I hung out on ClayArt, but it appears to have, well, died? Ah well. So happy to find this spot - I've already had many questions answered, just via searches.

Five years ago, I converted a small electric kiln to a soda, fired with a 20-lb tank of propane and a Venturi burner. I only fired it three times, at 9 months pregnant, before falling off the cliff of parenthood.

I've since acquired a 7-cubic-foot Paragon, from which I tore out the elements and am planning to drill a few holes, spray in some ITC, and give it a go again with the same burner. Mark Ward assures me I will be able to fire it to Cone 6 with two connected 40-lb tanks. But. This is summer only. He also assures me it will not work in winter.

He gave me his explanation of *why* while I was stirring three pots, holding a two-year-old, and shooing away a five-year-old. So I'm not sure if I get it: Do I just need more propane to fire in the winter? Is that the only issue? I can't go any bigger with tanks without bringing in far too many ruling authorities. Could I just string four of them together? Is there a magic way of making this project work? I'm not going to be out there freezing my arse off, firing the kiln at -30 (C or F) anyway, so we're just talking about mild winter temps, say high 20s.

Can I really not do this? It's, um, fairly central to my entire new game plan.

My guess is its so cold the tank valves will freeze up. If you could keep them warm then they will not freeze up as fast.Its sounds to cold to run water over them and too large to keep underwater-maybe a trickle of warm water on valve tops.
Lets see what cold winter folks say.
Mark

I have heard people using electric blankets to keep their tanks warm. I have never tried that. I have fired with 100 gallon tanks in up state NY many years ago and I did use hot water on the tanks. There is probably a certain level of cold that prohibits the vaporization of the propane. When you hit that level and if you are sucking out the propane vapor faster than it can vaporize, you get freezing tanks.
Mark knows his stuff. He has custom plumbed my burners for four tanks per two burners for my raku setup.
Trust him.
Marcia

Oh, I definitely trust him. I just didn't want to bug him to explain it to me again - I think I had him repeat it twice on the phone. I thought if I came here we could brainstorm something else to do. Last night I fell to sleep *convinced* I was going to tear up another little kiln, connect them, and fire with wood ...

It is about the vaporization rate, not the volume of liquid gas available. When you are firing to something like 2200 F, whether the kiln chamber is starting out at minus 20 F or +80 F is really not of any real significance.

Unless you use some specialized burners called "liquid withdrqawal burners" (one potential but expensive option for you) your burners are combusting gaseous propane. But the "store" of propane in the metal tank(s) is in the liquid form (hence LPG or liquid propane gas). So in order to burn the fuel, it first has to evaporate as a gas off the exposed surface of the liquid into the space above it in the tank, from where you withdraw it via the fittings that are controlled by the tank valve.

The smaller the surface area from which to evaporate, the less propane as a gas will evaoprate in a unit of time for a specific temperature of the liguid propane material. Small verrtical tanks have small surface areas exposed for this function. This is why for kiln use people often (in the USA) use horizontal cylindrical tanks. For a "gas geill type" tank, basically this surface is the interior diameter of the given tank you are using. For a given tank size, stringing two tanks together gives you twice the evaporation surface to work with. Stringing three tanks together gives you three times the surface area. And so on. So that is one place to "go" to solve this. But likey that is not totally enough.

The next factor is the main big issue of concern for you.

When you evaporate a liquid into a gas it requires heat energy to do so. As heat energy is utiized to cause evaporation off the surface, the store of liquid gas cools down. Evaporation rate from a specific amount of surface area is directly dependent on the temperature of the liquid stoage of gas. As the temperature of the liquid store goes down... the amount of gas evaporated in a unit of time (from a given surface) decreases. As you continue to draw evaporated gas from the tank, uless there is some means of adding some heat energy back into the liquid store.... it steaily continues to cool down.

The way heat energy gets into the store of liquid gas in a propane tank is from heat transfer from the surrounding air into the metal tank walls and hence into the liquid gas. The warmer the ambient air, the more heat energy in a unit of time gets "into" the liquid gas store. So in the cold Canadian winters, there is little driving force to transfer much he at into the liquid. THAT is the issue here.

You need to size the tank installation so that for the given size kiln the evaporation rate will not cause the overall storage of propane, when ALSO looking at the evaporation surface area available, to no longer support the evaporation rate for the volume of gas to support the peak BTU draw of the burners throughout the entire firing.

So lets say if your kiln requires an input of 100,000 BTUs per hour at peak firing rate (top end of the firing) then you need to make sure that given the ambient expected minimum temperature of the environmen,t that the storage you select will support this evaporation rate for sustaeained periods.

This is not a difficult problem to solve. Your propane supplier can calculate this for you based upon the surface areas of the tanks you use plus the volume of liquid in them. I don;t have time right now to do this for you.... but it is a pretty simple calculation. Likely you will have to string together an array of those 40 lb. cylinders to get the surface area and the liquid volume necessary to not cool too much before the kiln is done firing. Without doing the math.... I'm guessing that 4 tanks (maybe 5) will do it.

PS: It is also possible to keep the heat trransfer into the liquid store higher by using a bath of WARM (not hot) water to heat up the tanks during firing. But be VERY careful with this approach. As the temperature of the tank surface comes up, and hence the liquid gas does too, because evaporation rate increases the tank gaseous PRESSURE comes up also. Apply too much heat too fast and you can exceed the tank's rated pressure hoding capacity. Plus there is a "high pressure relief" valve on most tanks these days... that will vent raw propane gas if the pressure gets too high (to prevent tank rupture).

Great link and much more in detail than my explanation.
I have 2 40 pound tanks for each of my two burners and they do not freeze, but after living in Montana I am now living in the tropics. The chart in the link is great for really grasping what is happening with the vaporization.
Thanks, John.
Marcia

I fired a gas kiln through the last two winters in central PA - probably not as cold as Canada, but I think at least one of my final solutions would work. I tried an electric blanket, and heat tapes - neither provided enough heat/contact for a 100lb tank. Currently, I use one 40 lb tank and either use a small round sprinkler to run water down over it, OR submerse it in water while firing. We rigged a 30 gal trash can with an overflow at the top, and feed the hose to the bottom and run a VERY SMALL constant flow, just to keep the water moving a bit. We also had to rig a non-float device (in our case, a piece of plywood with a hole for the top of the tanks, strapped to the handles of the trash can. The overflow allows you to put a pipe on it to flow the water away from where you're working, so you don't end up with freezing patches to walk through. Since it's not pressurized, I don't glue those joints, and I can put it all away when not firing. Hose in the basement, so it doesn't freeze up, and all other pieces drained.

Just typing that makes me so happy my electric kiln is up and running. Gas is fun, but there was a lot of work involved.

Alice,
That is an interesting solution. I am always impressed with how people come up with such a wide variety of solutions to a single problem.
That is what makes these forums so beneficial to everyone.

After a long hiatus from pottery, I'm attempting to get a studio up and running again (shed is built and sided, just need a roof and some power - it's getting exciting!). At one time I hung out on ClayArt, but it appears to have, well, died? Ah well. So happy to find this spot - I've already had many questions answered, just via searches.

Five years ago, I converted a small electric kiln to a soda, fired with a 20-lb tank of propane and a Venturi burner. I only fired it three times, at 9 months pregnant, before falling off the cliff of parenthood.

I've since acquired a 7-cubic-foot Paragon, from which I tore out the elements and am planning to drill a few holes, spray in some ITC, and give it a go again with the same burner. Mark Ward assures me I will be able to fire it to Cone 6 with two connected 40-lb tanks. But. This is summer only. He also assures me it will not work in winter.

He gave me his explanation of *why* while I was stirring three pots, holding a two-year-old, and shooing away a five-year-old. So I'm not sure if I get it: Do I just need more propane to fire in the winter? Is that the only issue? I can't go any bigger with tanks without bringing in far too many ruling authorities. Could I just string four of them together? Is there a magic way of making this project work? I'm not going to be out there freezing my arse off, firing the kiln at -30 (C or F) anyway, so we're just talking about mild winter temps, say high 20s.

Can I really not do this? It's, um, fairly central to my entire new game plan.

Propane in the tank is liquid and must boil ( ie chang state to gas ) to be used. This is achieved on warm days by absorbing heat from the atmosphere as it boils and changes to gas the pressure rises. In cold temperatures it will simply stay liquid at atmospheric pressure. As the level drops in the tanks the surface area of the liquified gas reduces and thus the area to absorb heat reduces and the problem gets worse. I know we struggle here in England where temperatures are unpleasant but warmer than Canada. Can you keep the cylinders inside? You can heat gently by running hot water over the cylinders but do not try direct heat , I know or rather knew somebody who tried that - he is no longer with us!. We solved the problem by getting a bulk tank about 3 cubic metre but even this ends up with a covering of ice if the ambient temberature drops near to but above freezing. Good luck

Oh, my. Now I see why I didn't grasp the explanation when I was so distracted. I'm still not completely there - I'm printing out your explanation, John, to sit down by the fire and digest it properly. Thank you so, so very much.

The general recommendation to keep the tanks warm made me think - could I just place them inside the studio while I'm firing? It won't be too awful far from the kiln (~10-15 ft). Just run a longer hose to the burner?

But Google tells me it's horrifically dangerous and illegal to store propane tanks indoors, or even in garages. This is a matter of the tanks leaking and the gas not being able to dissipate, but instead being trapped inside the building, correct? Would the danger still be as high if I only had them indoors for an 18-hour firing period?

The safety issue with propane is its a heavy gas-that is it settles in the lowest area and hangs there. So lets say it was stored inside and had a leak that gas accumulates in lowest past of that building and waits for an ignition . As its heavy it does not dissipate easy or fast.
Bringing it inside has its own issues which can be worked out but you need to know about how and why propane does what it does.
I like the underwater tanks or slow trickle of water to cure the freeze up.

It almost sounds like you could rig up a water pump from a fountain that would recirculate the water that the propane tank sits in . . . would eliminate the need for run-off hose and make better us of water.

It almost sounds like you could rig up a water pump from a fountain that would recirculate the water that the propane tank sits in . . . would eliminate the need for run-off hose and make better us of water.

This is a great idea-The pumps are very small and cheap-put the tank on a large plastic trash can lid or the like-fill with water a few inches drop pump into water run small tubing to tank valve and it will pump away as water drains back into lid over tank.You may have to start with warm water so it does not freeze right away.Mark

The fella who built my pottery shed wants to build a tiny little doghouse-sized "pump house" for the tanks. Walls and roof, a little baseboard heater to keep the temp just above freezing while firing the kiln. I suggested leaving an inch or two gap at the base of the walls - to let trapped propane escape, if there were to be a leak.

I don't know enough about this to really comment, but,I think that LPG is made up of propane and butane. Propane boils off at something like -40 deg. F. and butane boils at around freezing. If you use small tanks in sub-zero temps you will use up the propane, but not the butane. If you don't completely empty the liquid you will end up with only butane in them and it won't produce the gas you need or the pressure to push it out of the tank.

Just brain storming, but I'd try to use the heat of the kiln to warm the tanks. Perhaps run some copper tubing around the stack and circulate water into a tub with your tanks in it. If you could get a variable speed pump you could then find a rate of transfer that didn't outpace the tanks and risk overwhelming the pressure relief valves. And, the heating would be regulated by the process.

The problem with freezing tanks won't be solved by keeping them only 'just above freezing', we regularly manage to freeze tanks doing raku outdoors here on the Oregon Coast even with the air temperature in the 50s. Running water over the tanks is actually a common solution, I'm not sure why it scares you! Can't really give you any good answers, I just know we froze a tank a couple weeks ago, very annoying!